1. Field of Invention
The invention relates to a network apparatus and, in particular, to a power network apparatus.
2. Related Art
The HomePlug apparatus is a network apparatus. The terminals of the HomePlug apparatus communicate with each other through power lines for supplying power, and data transmission is performed through the power lines. Thus, the trouble of arranging network wires and layout can be avoided at homes, schools, and companies.
Because noise exists on the power lines, the carrier sense multiple access with collision avoidance (CSMA/CA) of IEEE 802.11 serves as the media access method and the frequency band (from 4.3 to 20.9 MHz) with the less noise on the power lines is used for the data transmission in a power network. In addition, the power network increases the transmission speed and the ability against the interference by the way of orthogonal frequency division multiplexing (OFDM) modulation.
Generally speaking, the power lines may have a surge generated due to the factor such as a thunderbolt or interference. In order to prevent the impact caused by the surge, a surge protecting circuit is usually provided to absorb the surge.
Referring to FIG. 1, a conventional power network apparatus 1 includes a power network processing circuit 11, two capacitors 12 and 13 and an arrester 14. The power network processing circuit 11 is electrically connected to a power network 2 to receive/transmit an information signal, and demodulate/modulate or decode/encode the information signal so as to reproduce a data signal from the information signal or to mix the data signal into the information signal. The power network apparatus 1 may provide the data signal to a computer, a digital home appliance or a calculator apparatus.
The capacitors 12 and 13 and the arrester 14 serve as a surge protecting circuit and are disposed between the power network processing circuit 11 and the power network 2. The first ends of the capacitors 12 and 13 are electrically connected to a node S, and the second ends of the capacitors 12 and 13 are electrically connected to two ends of the power network 2, respectively. One end of the arrester 14 is electrically connected to the node S and the other end thereof is electrically connected to the ground. The surge on the power network 2 may be properly buffered and guided to the ground through the capacitor 12 and the arrester 14 or through the capacitor 13 and the arrester 14. Thus, it is possible to prevent the surge from being inputted to the power network processing circuit 11 to damage the circuit.
Under this architecture, however, the capacitors 12 and 13 may absorb the information signal on the power network processing circuit 11 and the power network 2 so that the intensity of the information signal is attenuated and the data transmission rate is decreased and the data transmission quality is influenced.
Therefore, it is an important subject to provide a power network apparatus capable of preventing the above-mentioned problems from happening and improving the above-mentioned drawbacks.